Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $90.92   4.829%   $95.3105   $95.31   $95.30   $95.30  
  Purchase #2 $173.25   6.605%   $184.6932   $184.69   $184.70   $184.70  
  Purchase #3 $105.83   13.398%   $120.0091   $120.01   $120.00   $120.00  
  Purchase #4 $234.66   5.642%   $247.8995   $247.90   $247.90   $247.90  
  Purchase #5 $219.69   5.813%   $232.4606   $232.46   $232.45   $232.50  
  Purchase #6 $107.72   6.582%   $114.8101   $114.81   $114.80   $114.80  
  Purchase #7 $173.99   12.355%   $195.4865   $195.49   $195.50   $195.50  
  7 purchase totals = $1,106.06       $1,190.6695   $1,190.67   $1,190.65   $1,190.70